Keeping the rain out

I have the doors and top off for the summer, and the Jeep lives outside. I bought a regular car cover, but it promptly ponds and leaks into the Jeep in moderate rain. My temporary solution was to throw a scrap piece of plywood on the sport cage under the cover, but am looking for a more elegant solution.

What are people using and does it work?

Not just in an emergency during a shower on the road, but longer term, overnight, over a week, etc…